There are only a handful of companies that build frames.
I think the more correct answer is there are hundreds of companies that have a few companies making their frames. For all but the high-end bikes you would really have to do some serious research to find out who actually made what bicycle. What you are really buying is a particular logo and branding that appeals to you. Much like choosing between Nike and Adidas shoes both of which are manufactured by nameless offshore sweatshops, in various parts of Asia.
Surly, in their blog, states that they tried to find a USA manufacturer to work with them, but no one showed much interest and had to go to Taiwan. Even top-end lines like Rivendell with the appearance of American made are almost entirely made in Asia.
I ride a Bianchi Axis, which is a step up from the popular Volpe, but shares the same basic cyclocross geometry albeit with an aluminum frame. My Axis was produced and assembled in an Export Processing Zone (EPZ) in Taiwan. The following is its lineage as far as my research has been able to inform me. (Others are welcome to correct or make additions.) The aluminum tubing was made in the United States Easton, the carbon fiber forks were produced in Japan - probably Toray Composites. The drive train and other components are Japanese and Taiwanese with some of the parts subcontracted to Indonesia - Shimano, Sugino and Sram. The wheel sets and tires were junk from Korea and subject to a recall. The SPD compatible pedals were of unknown origin and fell apart quickly.
It was designed by a woman, Sky Yaeger, AKA Chick Design, an employee of Bianchi USA, in Hayward CA, which is a licensed logo branding agent of the F.I.V. Bianchi Company, which is wholly owned subsidiary the Cycleurope Group, which is controlled by the Swedish holding company Grimaldi Industri AB. Bianchi no longer exits as a bicycle manufacturer, but my bike came with eleven (11!) official, brightly displayed, Bianchi logos.
I think you will find a similar maze for most lower and mid level bikes on the market today. If we get too loyal to a particular brand then we have been had.
All that said I love riding my bike.
Western Flyer
A wise traveler has no fixed plans and is not intent upon arriving.
Lao Tzu